79/80-(3/16+39/80)=5/16
3/16+39/80=(3*5+39)/80=54/80
79/80-54/80=(79-54)/80=25/80=5/16
2/45+(41/45-7/9)=8/45
41/45-7/9=(41-7*5)/45=6/45
2/45+6/45=(2+6)/45=8/45
7/15 -(2/15+1/5)= 2/15 (здесь знак пропущен?! я поставила -)
2/15+1/5=(2+1*3)/15=5/15
7/15-5/15=(7-5)/15=2/15
3/16+(15/16-5/8)=
15/16-5/8=(15-2*5)/16=5/16
3/16+5/16=(3+5)/16=8/16=1/2
